Apparatus and method for direct vertebral rotation

ABSTRACT

An instrument for spinal rotation that aligns and holds direct vertebral rotation (DVR) lever arms relative to each other to achieve an initial axial alignment of a segment of vertebrae and allows the final DVR rotation by rotating the instrument and lever arms together. A method of direct vertebral rotation that allows rotating the vertebrae to be aligned relative to each other, and collectively rotating the vertebrae to be aligned relative to adjacent spinal segments by rotating the direct vertebral rotation instrument. A system for direct vertebral rotation having at least two pedicle screws. The system also includes at least two levers attachable to the pedicle screws and a clamping instrument configured to clamp the levers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/383,006, filed on Dec. 19, 2016, which is a continuation of U.S.application Ser. No. 13/889,847, filed on May 8, 2013, which is adivisional application of U.S. application Ser. No. 12/152,834, filed onMay 16, 2008, which claims the benefit of the filing date of U.S.Provisional Patent Application No. 60/930,770, filed May 18, 2007, thedisclosures of which are hereby incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to an alignment linkage such asa direct vertebral rotation instrument for creating, restraining and/ormaintaining horizontal rotation of the vertebrae during posterior spinalfusion operations. The present invention also relates to a method forcreating, restraining and/or maintaining horizontal rotation of thevertebrae during posterior spinal fusion operations.

BRIEF DESCRIPTION OF THE PRIOR ART

During spine surgery for conditions such as scoliosis, the surgeon seeksto achieve a three-dimensional correction of the spinal column shape byrealigning and instrumenting the vertebrae in order to achieve aneventual fusion of the vertebral bodies in the desired alignment.Typically, the misalignment of the patient's vertebral bodies is readilyapparent in the sagittal and coronal planes, either visually or byradiography. More difficult to see and correct is rotationalmisalignment of the vertebrae about the axis in the defined along thelength of the spine. This rotation is often characterized in thescoliosis patient by projection of the ribs of the back creating aso-called rib hump on one side of the back caused by the rotation of thethoracic vertebrae and the attached ribs. While the axis of rotationactually changes along the length of the spine due to the spines naturalcurvature, for convenience of discussion the axis will be discussed asif it is a vertical line.

In order to correct such a rotational misalignment, the surgeon mustaxially rotate the vertebrae in the opposite direction so that they arecorrectly oriented about the longitudinal axis of the spine. Acorrective rotation of this type is often referred to as a “derotation.”

Direct vertebral rotation, hereinafter “DVR,” is one method ofhorizontally rotating and re-aligning vertebral bodies. To use DVR,screws are implanted in the pedicles of the vertebrae and then ahorizontal torque is applied by a lever arm or extension tube mounted tothe screw head. As mentioned above, the indication is frequentlyscoliosis, but other deformity issues may be addressed through DVR.Tubular lever arms are then placed on the screws in line with the axisof the screw. A force is then applied to the lever arms to rotate thespinal vertebrae. This brings the vertebrae into the desired positionsand in line with one another. The surgeon and the surgeon's assistantsface the difficult task of manually rotating and aligning the variouslever arms to eventually fasten the pedicle screw assemblies to rods andform a construct holding the vertebrae in the desired alignment.

Polyaxial pedicle screw assemblies have, by way of example, a cageshaped to receive a bone screw, a rod and a blocker or set screwengaging screw threads. Generally, cages have two arms that extend awayfrom the screw and define a slot through which the rod can passtransverse to the axis of the cage. Often, such cages are referred to astulip shaped. The cage can move polyaxially about the head of the bonescrew until the assembly is fixed in a position. Once the rod is inplace, the blocker is threaded within or on the outside of the cage. Theblocker engages, directly or indirectly, the rod which in turn engagesthe head of the bone screw seated in the cage or engages the cageitself. The blocker thus locks or immobilizes the assembly.

A monoaxial pedicle screw assembly generally includes a bone screw withan integral cage or head to receive the rod and blocker or nut.

For DVR, the lever arms apply torque to the bone screw and the bonescrew, in turn, applies the torque to the vertebrae. Either a polyaxialor monoaxial screw assembly may be used. The lever must fit tightly andgrasp the screw head in order to apply the torque. If a polyaxial screwassembly is used, the head should be immobilized in the direction ofaxial rotation to allow the transmission of torque. A polyaxial screwalso has a limited extent of free travel and can create torque on thevertebra once the range of movement of the head is exceeded.

SUMMARY OF THE INVENTION

The present invention fills the need described above by providing asystem and method for rotation of vertebral segments for posteriorspinal fusion.

The invention is directed to an instrument and associated method thataligns and holds the DVR lever arms relative to each other to achieve aninitial axial alignment of a segment of vertebrae and allow the DVRrotation by rotating the instrument and lever arms together.

Joining the lever arms or extension tubes with such a clampinginstrument allows the surgeon to more uniformly and easily rotate thetubes together and to stepwise achieve a relative orientation of asegment of vertebrae. The segment of vertebra to be aligned can bealigned collectively relative to adjacent spinal segments.

In one aspect the invention teaches a method of direct vertebralrotation, wherein the steps include attaching pedicle screws to at leasttwo vertebrae to be aligned and attaching a lever to each of the pediclescrews. The levers are positioning between jaws of a direct vertebralrotation instrument and the jaws held in closed position. The jaws arebrought together to rotate the vertebrae to be aligned relative to eachother, and the vertebrae to be aligned are collectively rotated relativeto adjacent spinal segments by rotating the direct vertebral rotationinstrument.

In another aspect the invention teaches a direct vertebral rotationinstrument comprising a first jaw; a second jaw; a hinge connecting thefirst jaw and the second jaw; and a lock for locking the first jaw tothe second jaw.

In yet another aspect the invention teaches a system for directvertebral rotation having at least two pedicle screws. The system alsoincludes at least two levers attachable to the pedicle screws and aclamping instrument configured to clamp the levers.

In one aspect of the present invention, the instrument has substantiallyparallel jaws to engage or clamp the lever arms in relative alignmentfor manipulation.

In another aspect of the invention, the jaws of the instrument have acompliant material for interface with the lever arms in order to assistin gripping the lever arms and thus facilitate the effective adjustmentof the longitudinal position of the lever arms.

A further aspect of the invention includes the method of rotatingvertebrae located within a patient's body about the spinal axis by:implanting a first pedicle screw on a first vertebra; implanting asecond pedicle screw on a second vertebra; attaching a first moment armand a second moment arm to the first screw and the second screw,respectively; locking the first moment arm and a second moment arm in apreliminary angular orientation with respect to the spinal axis byapplying pressure using the opposing jaws of an instrument to align andrestrain said moment arms; and rotating the instrument, arms andvertebra relative to the spinal axis.

The present invention may be reduced to practice by a clampinginstrument which includes elongate jaws having opposed interior facesand being hingeably or rotatably connected at one end or interior fromone end, the jaws having an open position and a closed position, theopen position facilitating the instrument to be arranged about aplurality of pedicle screw extension tubes or other lever armsassociated with vertebra. The instrument in its closed position holdsand initially aligns the lever arms on the interior faces of the jaws.

In another aspect of the present invention, the above describedinstrument includes handles to facilitate at least the closing of thejaws. The handles may be in the central area of the jaws and extendtransverse to the elongate axis of the jaws, or may be displaced towardsor at one end of the jaws, or even as an extension generally inalignment with the elongate axis of the jaws, or a portion of the jawsthemselves may serve as portions of handles.

In another aspect of the present invention, the jaws are hingeablyconnected at one end or are located interiorly from one end and includea spring mechanism to hold the jaws in a normally open position. Thisnormally open position facilitates arrangement of the jaws about theextension tubes or lever arms to be clamped within the jaws. The hingemay be integral with one or both jaws, or may be a separate elementconnected to the jaws.

In another aspect of the present invention, the closing mechanism isprovided to hold the jaws in a closed position such that a surgeon orsurgeon's assistant does not need to hold the handles together in orderto maintain the instrument in a closed position. In one embodiment, aclosing mechanism may be a latching mechanism provided anywhere alongthe jaws, or even on the handles themselves. In a preferred embodiment,a latching mechanism is provided at the end of the jaws opposite thehinge mechanism, and comprises a pawl and ratchet arrangement whichautomatically latches the jaws as the jaws are closed. The latchingmechanism may have an extension with a finger grip, which may simply bea surface designed to facilitate gripping of one's finger (knurling,raised gripping ribs, etc.). The finger gripping portion may extendlaterally outside of one of the jaws such that a depression on thatportion will release the pawl and ratchet mechanism.

In another aspect of the present invention, the interior faces of thejaws have a surface to facilitate gripping the extension tubes or leverarms. In a preferred embodiment, this may be a compliant material suchas rubber. The coefficient of friction of such a material shouldfacilitate the gripping of the lever arms, and the material may alsoinclude compliancy such that the lever arms are, upon undergoing aclamping force, forced into the material for gripping purposes. Thecompliance also allows the lever arms to be gripped at various anglesand positions along the length of the jaws.

In another aspect of the present invention, a method includes the use ofthe above broadly described instrument by surrounding a plurality oflever arms with a normally open instrument, positioning the instrumentabout the lever arms, closing the instrument such that the jaws clampthe lever arms, and manually applying a torque and otherwisemanipulating the instrument in order to manipulate the lever arms andthus the vertebra to which the lever arms are connected, directly orindirectly. The clamping of the jaws may achieve an initial desiredalignment of the lever arms and vertebrae and then the entire assemblyof the lever arms and vertebrae may be further rotated to the finalposition. The method may also include the steps of fixing spinal rods orother fixation devices arranged with respect to the vertebra to maintainthe vertebra in the aligned position, and subsequently releasing theclamping instrument and removing the same from the lever arms.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic right side view of four adjacent vertebrae of aspine, with pedicle screws and lever arms as used in DVR.

FIG. 2 is a plan view as in FIG. 1 showing the lever arms andestablishing a coordinate system relative to the human body.

FIG. 3 is a schematic right side view of four adjacent vertebrae of aspine, with pedicle screws, lever arms and an instrument according tothe present invention.

FIG. 4 is a plan view as in FIG. 3 showing the lever arms and instrumentof the present invention.

FIG. 5 is a perspective left side view of four lever arms and aninstrument according to the present invention.

FIG. 6 is a perspective left side view of two lever arms and aninstrument according to the present invention.

FIG. 7 is a perspective view of an instrument according to the presentinvention in the open position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, the portion of the spine illustrated includes afirst vertebra 1 a, which may be the T10 (Tenth Thoracic) vertebra of apatient, a second vertebra 1 b, which may be the T9 (Ninth Thoracic)vertebra of a patient, a third vertebra 1 c, which may be the T8 (EighthThoracic) vertebra of a patient, and a fourth vertebra 1 d, which may bethe T7 (Seventh Thoracic) vertebra of a patient. The systems and methodsdescribed hereafter may be applicable to any vertebra or vertebrae ofthe spine and/or the sacrum (not shown). In this application, the term“vertebra” may be broadly interpreted to include the sacrum althoughrotation is only attempted relative to the sacrum and the sacrum itselfis not rotated.

Pedicle screw assemblies 11 a-11 d (collectively screws 11) areimplanted in the associated pedicles of the vertebrae 1 a-1 d. In one ofmany pedicle screw arrangements, pedicle screw assemblies 11 a-11 d eachhave a cage 13 shaped to receive a rod and a set screw that passesthrough an aperture of the cage. Each screw 11 also has a threaded shaft15 which is threaded into the vertebra 1 to implant the pedicle screwassembly.

Connected to the head 13 of each screw 11 are moment arms 21 a-21 d(collectively moment arms 21). In this embodiment the moment arms 21 arecannulated tubes having an open distal end 23 allowing placement ofobjects such as the aforementioned locking screws and suitable lockingscrew drivers through the cannulae of the tubes. These moment arms 21serve as lever arms in connection with the vertebral rotation systemherein. The proximal end 25 of each moment arm 21 removeably engages thehead 13 of the respective pedicle screw assembly 11 so as to be able toapply torque to the vertebrae 1.

FIG. 2 shows a top view, related to FIG. 1, of the distal end of themoment arms 21 a-21 d. Also shown is a coordinate system definingsuperior and inferior directions along the spinal axis and left andright directions in the plane defined by the spine axis A-A. Thus, thetorque to be applied by the moment arms 21 is in the left or rightdirection. It can be seen that the distal ends 23 of the moment arms 21are offset in various left-right and inferior-superior directionsdepending on the initial geometry of the patient's spine and the pediclescrew placements as determined by the surgeon.

FIG. 3 schematically illustrates an embodiment of a clamping instrument31 according to the present invention. The instrument 31 engages, alignsand restrains the positions of the moment arms 21 by clamping the arms21 in the distal region outside the patient's body.

FIG. 4 shows a top schematic view, related to FIG. 3, of the distal endof the moment arms 21 a-21 d and of the clamping instrument 31. Theinstrument 31 has longitudinal jaws 33 that are capable of being movedtoward and away from each other in the lateral left and right directionsto clamp onto the moment arms 21 and consequently align and restrainthem. Each jaw 33 has a compliant material 35, such as a polymer orrubber, to conform to each moment arm 21 and accept the arms at variousinferior-superior angles along the length of the jaws 35. The compliantmaterial assists in gripping the moment arms 21.

End portions 37 of the clamping instrument 31 connect the jaws 33 tocomplete an approximately rectangular structure having a central openingfor the moment arms 21. A first end portion 37 incorporates a hinge orother mechanism for allowing the jaws to come together and a second endportion 37 incorporates, in the preferred embodiment, a latchingmechanism or other closing mechanism that restrains the jaws 33 in theclosed position. The clamping instrument 31, once closed on the momentarms 21, are capable of being moved toward and away from each other inthe lateral left and right directions to align and restrain the momentarms 21.

The clamping instrument 31 has two different functions for aligning thevertebrae. The first alignment is achieved by the closing and latchingof the jaws 33 as shown by the relative rotations of the moment arms 21shown between FIGS. 2 and 4. Thus, moment arm 21 b is rotated leftwardrelative to arm 21 a, moment arm 21 c rightward relative to arm 21 b andso on. Consequently, each vertebra is rotated relative to adjacentvertebrae to achieve an initial rotation within the instrumented segmentof vertebrae. If straight moment arms 21 are used, the degree of initialrotation for each vertebra 1 depends primarily on the positioning andorientation of each pedicle screw assembly 11. If desired, a specialmoment arm 21 with an offset distal portion may be used to increase ordecrease the preliminary rotation of a given vertebra 1.

The second alignment is achieved by manually rotating the clampinginstrument 31 and the clamped moment arms 21 together to align theinstrumented spinal segment. Thus, the clamping instrument 31 canachieve rotation both on a vertebra-to-vertebra basis and of an entiresegment of the spine relative to the rest of the spine.

FIG. 5 shows a perspective view of a preferred embodiment of theinvention with the clamping instrument 31 restraining four moment arms21, each of which has a passage 27 at its proximal end to accommodate aspinal rod. Mounted to the longitudinal jaws 33 are handles 45. Thehandles 45 serve the dual purposes of assisting in the closing of thejaws for the initial rotation and then allowing manipulation of theentire instrument for the final rotation. The handles 45 may be placedin any suitable position on the clamping instrument 31. In theillustrated embodiment, the handles 45 are shown in a central location,but in other embodiments these may be closer to or at the latch endopposite the hinge end.

As also seen in FIG. 6, hinge 41 is at one end of the clampinginstrument 31, and a latch 43 is at the opposite end. In one embodiment,no latch is required as the handles can hold the instrument in theclosed position when being held by a surgeon or surgeon's assistant. Inanother embodiment, a latching device can be provided on or associatedwith the handles as opposed to directly on the jaws of the clampinginstruments.

As shown best in FIG. 6, the instrument 31 may accommodate the momentarms 21 at various angles in the inferior/superior plane. The resilientmaterial 35 assists in this regard as it conforms to and grips the arms21 at various angles. As shown, the instrument 31 may be also be used ina left-right orientation, and the moment arms 21 a and 21 d may beattached to pedicle screws on either side of the spinous process of thesame vertebra. This arrangement creates a triangulated structure thatcan apply a greater torque to a vertebra while decreasing the bendingmoment on the pedicle screws. This approach can be used in conjunctionwith a second instrument 31 oriented in the superior-inferior directionto first create an initial alignment using the first instrument 31 andthen restrain the vertebra with respect to other vertebrae using thesecond instrument 31.

FIG. 7 shows the clamping instrument 31 in an open position and moreclearly shows portions of its structure, particularly the hinge andlatching structures. In the preferred embodiment, a spring-loaded hingebiased toward the open position is employed. Also in a preferredembodiment, a spring-loaded ratchet and pawl type latch 43 is employed.Thus, one handed operation is facilitated. The clamping instrument 31can be arranged about the moment arms 21, i.e., extension tubes, closedand latched, all with one hand. Disengagement of the latch 43 isfacilitated by the latch extension and finger grip which lies outside ofone jaw. A simple depression of this extended finger grip portion willdisengage the ratchet and pawl arrangement.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention.

The invention claimed is:
 1. A system for direct vertebral rotation,comprising: at least two levers, each of the levers having an attachmentend attachable to a pedicle screw implanted in a vertebra of a spinesuch that each lever extends proximally from the respective pediclescrew, and each of the levers having a free end opposite the attachmentend; and a clamping instrument including an elongate first member and anopposing elongate second member; wherein the first and second membersare movable toward one another to a closed position in which a pluralityof the levers are clamped between the first and second members, thefirst and second members of the clamping instrument applying asufficient lateral clamping force to the plurality of the levers in theclosed position so as to align the free ends of the plurality of thelevers along a longitudinal axis defined between the first and secondelongate members and so as to hold each of the plurality of the leversin a respective fixed angle and position with respect to the clampinginstrument.
 2. The system of claim 1, wherein the levers comprisecannulated tubes.
 3. The system of claim 1, wherein the clampinginstrument includes a lock configured to latch the first and secondmembers together in the closed position such that relative movementbetween the first and second members is restrained.
 4. The system ofclaim 3, wherein the lock is disengageable by a latch extension having afinger grip.
 5. The system of claim 1, wherein the clamping instrumentincludes a hinge connecting the first member and the second member, andwherein the first and second members are rotatable relative to oneanother about the hinge.
 6. The system of claim 1, wherein the clampinginstrument includes a hinge connecting the first member and the secondmember, the first and second members being rotatable relative to oneanother about the hinge, wherein the clamping instrument includes a lockconfigured to latch the first and second members together in the closedposition such that relative movement between the first and secondmembers is restrained, and wherein the lock is positioned at an oppositeend of the first and second members from the hinge.
 7. The system ofclaim 1, wherein the clamping instrument includes handles configured tobe held in a hand.
 8. The system of claim 1, wherein the first memberincludes a first compliant material portion and the second memberincludes a second compliant material portion, and wherein the first andsecond compliant material portions are configured to engage theplurality of the levers when the first and second members are broughtinto the closed position, such that the first and second compliantmaterial portions conform to grip the plurality of the levers.
 9. Thesystem of claim 8, wherein the first and second compliant materialportions are made from a material selected from a group consisting ofpolymer and rubber.
 10. The system of claim 8, wherein the first andsecond compliant material portions of the clamping instrument areconfigured to grip the plurality of the levers at a variety of anglesand positions with respect to the clamping instrument when the first andsecond members of the clamping instrument are brought into the closedposition.
 11. The system of claim 8, wherein, when the first and secondmembers are in the closed position, the plurality of the levers arereceived in an elongate opening defined between the first and secondmembers, and wherein the first and second compliant material portionsextend along substantially the entire length of the elongate opening ina longitudinal direction of the elongate opening.
 12. The system ofclaim 8, wherein the first and second compliant material portions of therespective first and second members each define a substantially planarsurface facing towards the other of the first and second members, thesubstantially planar surfaces being substantially parallel to each otherwhen the first and second members are in the closed position.
 13. Thesystem of claim 1, wherein, when the first and second members are in theclosed position, the plurality of the levers are received in an elongateopening defined between the first and second members.
 14. The system ofclaim 1, wherein, when the first and second members are in the closedposition, the clamping instrument defines an approximately rectangularstructure.
 15. The system of claim 1, further comprising at least twopedicle screws, each of the pedicle screws having a threaded shaft forimplantation into vertebral bone and a cage shaped to receive a rod. 16.The system of claim 15, wherein the attachment end of each of the leversis adapted to be attached to the cage of the respective pedicle screw.17. The system of claim 1, wherein, when the first and second members ofthe clamping instrument are in the closed position, the respective fixedangles of the plurality of the levers are fixed within a plane extendingalong and including the longitudinal axis defined between the first andsecond members.
 18. A system for direct vertebral rotation, comprising:at least two elongate structures attachable to and extendable proximallyfrom pedicle screws implanted in respective vertebrae of a spine; and aclamping instrument including an elongate first member and an opposingelongate second member; wherein the first and second members are movabletoward one another to a closed position in which a plurality of theelongate structures are clamped between the first and second members,the first and second members of the clamping instrument applying asufficient lateral clamping force to the plurality of the elongatestructures in the closed position so as to grip and hold each of theplurality of the elongate structures in a respective fixed angle andposition with respect to the clamping instrument.
 19. The system ofclaim 18, wherein the first member includes a first compliant materialportion and the second member includes a second compliant materialportion, and wherein the first and second compliant material portionsare configured to engage the plurality of the elongate structures whenthe first and second members are brought into the closed position, suchthat the first and second compliant material portions conform to gripthe plurality of the elongate structures.
 20. The system of claim 19,wherein the first and second compliant material portions of the clampinginstrument are configured to grip the plurality of the elongatestructures at a variety of angles and positions with respect to theclamping instrument when the first and second members of the clampinginstrument are brought into the closed position.
 21. The system of claim18, further comprising at least two pedicle screws, each of the pediclescrews having a threaded shaft for implantation into vertebral bone anda cage shaped to receive a rod.
 22. The system of claim 18, wherein,when the first and second members of the clamping instrument are in theclosed position, the respective fixed angles of the plurality of theelongate structures are fixed within a plane that is defined between andextends alongside the first and second members in the closed position.